1. Technical Field
The present invention relates to a spray gun usable with a module including a removable, easy-to-view, high-accuracy digital pressure gauge being installed in the spray gun as necessary.
2. Description of Related Art
The air spray gun uses compressed air to atomize a paint for spraying an object to be coated. To assure a stable quality of painting with the spray gun, it is necessary to always monitor and control the pressure of spraying compressed air. There are available some spray guns in which the spraying air pressure can be checked by the user operating the spray gun.
In the spray coating, both the quality of the finished coating and scattering of the paint mist greatly depend upon the spraying air pressure used in the air spray gun to spray paint on an object. Namely, it is well known that a higher air pressure will provide an increased energy for spraying and a finer atomization of the paint, which has generally contributed to an improved quality of paint coating. However, fine atomized mist of a paint is easily influenced by air flow to be more scattered. On this account, it is advisable to use a spray gun with an appropriate spraying pressure selected in accordance with the paint, object to be coated and coating conditions. For a quality spray coating, the spray gun should desirably be operated while monitoring the air pressure used for the spraying and under well-controlled conditions. In the recent spray guns, a lower air pressure is used to prevent the spray of paint from scattering, and thus because even a small change of the air pressure has a great influence on the coating quality, it has become more important to control the spraying air pressure.
Conventionally, the spraying air pressure is adjusted by a reducing valve or the like, and supplied through an air hose to the spray gun. During spraying of a paint, the user of the spray gun rarely checks the pressure of the air pressure. Recently, however, more and more air spray guns use a lower air pressure, and thus it has become important to adjust the air pressure within a lower pressure range and check the air pressure at hand.
Further, to assure a stable quality of painting and a quality skimming-coating of information devices and precision devices with a reduced amount of paint, it has become essential to appropriately control the paint spraying conditions.
Normally in the spray-coating tests, a spray gun is used with a pressure gauge being attached directly to the spray gun. In such tests, a general-purpose pressure gauge is connected to an air hose of the spray gun. However, the pressure gauge is rarely used in actual spray-coating because its weight and size are not acceptable in the routine paint spraying jobs.
It has been proposed to use a small pressure gauge installable directly to a spray gun and which permits the user of the spray gun to check the air pressure at any time in spraying a paint and will not interfere with the operation of the spray gun itself (cf. Japanese Published Examined Utility Model No. 22277 of 1993). This pressure gauge is an analog-indication one of a so-called Bourdon tube type. However, since the pressure gauge has to be designed smaller for installation to a spray gun which is normally not so large, such a pressure gauge is not satisfactory with respect to accuracy and durability in the operating environments.
Also, a spray gun with a digital-indication gauge using a pressure sensor is known from the disclosure in the Japanese Published Unexamined Utility Model No. 506310 of 1993. In this pressure gauge, a pressure gauge unit is housed in a closed container. When the service life of the driving cell has expired, the pressure gauge itself has to be discarded and replaced with a fresh one, which will lead to wasting of resources and addition of wastes.
The digital pressure gauge detects a pressure in an air channel and indicates it digitally, and this technology is already used in the general-purpose digital pressure gauge. The general-purpose digital pressure gauge includes a compressed air intake, pressure sensor, digital converter, indicator and a power unit, and it is used as an accessory to a spray gun. However, the pressure gauge thus used on the spray gun will add to the size and weight of the spray gun, which will cause increased fatigue of the user of the spray gun and will adversely affect the operability of the spray gun itself.